Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
  • H01B1/12—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances organic substances
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
  • B05D5/12—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain a coating with specific electrical properties
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
  • C09D5/4476—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications comprising polymerisation in situ
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers

Definitions

• the present invention relates to a method of grafting and growing a conductive organic film on a surface, to the film obtained by said method. It also relates to the use of the process and the film of the present invention in various applications such as the protection of surfaces against chemical attack, the manufacture of localized conductive coatings, the manufacture of chemical sensors, for example in the fields of chemistry and molecular biology, manufacturing of biomedical equipment etc.
• these films can be obtained on any electrically conductive or semi-conductive surface, by electroreduction of diazonium salts, and in particular of aryl diazonium salts, in an organic solvent or else in aqueous solution.
• Electro-reduction can be carried out under voltammetric, potentiostatic or intensiostatic conditions. It delivers organic films grafted onto the work surface, the thickness of which is greater than a monocular monolayer.
• thickness greater than a molecular monolayer By thickness greater than a molecular monolayer, one understands thicknesses greater or even much greater than the size of the molecular precursor, taken in its largest dimension, which has given birth of electro-grafted organic film.
• the embodiments specified below show for example that it is possible, starting from 4-nitrophenyl diazonium tetrafluoroborate having a size of approximately 1.5 n, to obtain films with a thickness of 100 hm or more.
• Conductive polymers are currently experiencing significant growth. They were recently honored by the Nobel Prize in chemistry awarded to Mac Diarmid et al [1]. These polymers can be obtained in film-forming form on conductive surfaces by electropolymerization of precursors such as pyrrole, aniline, thiophene, EDOT, etc. It is to these compounds that we will refer when we speak, in the following, of "traditional conductive polymers”.
• This electropolymerization consists of an electro-oxidation of the precursor, which can then dimerize to form an electro-oxidizable compound, which can therefore itself be electro-oxidized before dimerizing, and so on.
• the formation of a film proceeds by precipitation of the conductive polymer on the surface, when a critical concentration is obtained at the surface / solution interface.
• the films of conductive polymers obtained by electro-polymerization are therefore not grafted onto the surface.
• the films of traditional conductive polymers are produced by means of electro-oxidation of the precursors and their successive oligomers, they can only be obtained by anodic polarization of the surface on which the film is to be deposited: the noble metals or alloys being the only ones able to withstand anodic polarization without being oxidized and seeing their surface dissolve in the solution, traditional conductive polymer films can only be formed on surfaces of metals or noble alloys, such as gold or platinum.
• the present invention provides a method of grafting and growing a film of an organic conductive polymer on an electrically conductive or semiconductive surface which constitutes a solution to the aforementioned problems of the prior art.
• the process of the present invention is carried out by electroreduction of at least one diazonium salt precursor of said organic film, comprising a step of grafting and growth of the film by application of at least one protocol consisting in electroreduction of said diazonium salt on said electrically polarized surface at least one working potential more cathodic than the electroreduction potential of the diazonium salt, said potentials being measured with respect to the same reference electrode.
• these films are obtained by cathodic polarization of the surface. This polarization is measured relative to a reference electrode, for example a silver electrode.
• films of conductive polymers such as those based on pyrrole, aniline, thiophene, EDOT, etc., were obtained by the anodic route.
• the process of the present invention meanwhile gives access to both the surfaces of noble metals, such as gold, platinum etc., and to "non-noble" surfaces, such as surfaces with reducible oxide, a surface graphite, an organic conductive or semi-conductive surface, an alloy surface, a surface of a traditional conductive polymer (s) such as a pyrrole-based surface, aniline , thiophene, EDOT, acetylene, polyaromatics, etc., a surface of a semiconductor, intrinsic or doped, and any combination of these compounds.
• noble metals such as gold, platinum etc.
• non-noble surfaces such as surfaces with reducible oxide, a surface graphite, an organic conductive or semi-conductive surface, an alloy surface, a surface of a traditional conductive polymer (s) such as a pyrrole-based surface, aniline , thiophene, EDOT, acetylene, polyaromatics, etc.
• a traditional conductive polymer such
• the method of the present invention consists, unlike the methods of the prior art, in producing conductive coatings, that is to say electronic states delocalized on an initial surface having electronic states delocalized.
• the films obtained also have the advantage of resisting rinsing, and in particular rinsing under ultrasound, and are chemically grafted onto the surface of the working electrode.
• the conductive organic films can be obtained by electro-reduction of a diazonium salt or of a mixture of diazonium salts of generic formula R'-N 2 + , X " , in which the group R ' contains one or more aromatic cycle (s) and / or one or more group (s) unsaturated (s) capable of delivering conductive structures, and X " is a counterion.
• the groups R ′ may comprise an organic or inorganic group chosen from the groups nitro, fluoro, bromo, chloro, iodo, thiocyanato, sulfate, sulfonate, sulfonium salts, phosphate, phosphonate, phosphonium salts, salts of diazonium, amino, ammonium, alcohol, aldehyde, ketone, carboxylic acid, ester, amide, nitrile, anhydride, acid halide, as well as among the alkyl, alkenyl, alkynyl, aryl, naphthyl, anthryl, pyryl or polyaromatic groups of higher degree, themselves possessing one of these groupings.
• R ′ can be chosen, for example, from the following compounds a) to f):
• R, R 1 and R 2 when present, independently represent any organic or inorganic group, chosen for example from nitro, fluoro, bromo, chloro, iodo, thiocyanato, sulfate, sulfonate, sulfonium salts, phosphate groups , phosphonate, phosphonium salts, diazonium salts, a iné, ammonium, alcohol, aldehyde, ketone, carboxylic acid, ester, a ide, nitrile, anhydride, as well as among the groups alkyls, alkenyls, alkynyls, aryls, naphthyls, anthryls , pyryls or aromatic of higher degree, having one of these groups and / or other organic functions such as an amin, an ammonium, an alcohol, an aldehyde, a ketone, a carboxylic acid, an ester, an amide, a nit
• R ′ contain one or more aromatic heterocycle (s), such as pyridine or orthophenanthroline
• metal salts in the synthesis medium, so that they are complexed by said heterocycles, provide additional doping and can contribute to further enhanced electrical conductivity.
• Electrografting conductive organic films have been obtained by the inventors both with substituted aromatic diazonium and with unsubstituted aromatics.
• the diazonium salts can for example be in the form of tetrafluoroborates, halides, sulfates, phosphates, carboxylates, perchlorates, hexafluorophosphates or a mixture of these salts. From the results mentioned below, it appears that the increase in film thickness according to the process of the present invention depends in particular on the diazonium salt used. It can however be estimated that the resolution on the adjustment of the thickness according to the method of the invention is of the order of a few nanometers per scan.
• a support electrolyte can be added to the reaction medium to facilitate the passage of electric current through the solution, such as, for example, the tetraethyl ammonium perchlorate.
• the electro-reduction can be carried out on a conductive cathode, preferably in a solution, organic or aqueous, containing the diazonium salt (s), at a concentration which can be for example between 10 ⁇ 4 and 1 mol / 1.
• the grafting and the growth of the film take place on the cathode as soon as its potential is greater, in absolute value, than the electro-reduction potential of the diazonium salt, compared to a reference electrode.
• the inventors have observed that it is possible to obtain a rapid and uniform grafting in thickness surprisingly by imposing on the surface on which the film is grafted a potential more cathodic than the diazonium electroreduction potential.
• the electroreduction potential of the diazonium salt can be applied in different ways, called “potential application protocols” below:
• a reference electrode for example a silver electrode, that is to say to the value defined according to the present invention. It is a protocol applied in potentiostatic mode referenced.
• At least one protocol can be applied in potentiostatic mode, and / or in intensiostatic mode.
• the working potential can be variable and / or a variable working current can be imposed on said surface.
• the film can be grown by successive application of several protocols, chosen independently from protocols with fixed or variable imposed working potential and protocols with fixed or variable imposed working current, each protocol being applied to said surface for a determined duration identical or different from that of the other protocols.
• all the protocols applied to said surface can be identical.
• the grafting and the growth of the film can be obtained by a combination of protocols with fixed or variable imposed potential and protocols with fixed or variable imposed current.
• the potential of said surface can be imposed so as to form a triangular niche of potential.
• a triangular current slot can be imposed on said surface.
• the potential of said surface can be imposed so as to form a square niche of potential.
• a square current slot can be imposed on said surface.
• the inventors have in fact demonstrated that it is possible, unexpectedly, to further increase the thickness of the organic film obtained by the process of the present invention, by repeating several times, successively, application protocols. of potential or current as described above.
• the growth of the film in thickness is obtained and can be controlled by application of one or more protocol (s), leading to the desired potential, until the desired film thickness is obtained.
• the number of protocols applied for grafting and growing the conductive organic film depends on the objective sought in the context of the present invention. It can vary, for example, from 1 to 10,000.
• the duration of an application protocol also depends on the desired film thickness. It is generally for example from 1 to 500 seconds. Those skilled in the art will be able to adapt this duration according to the objective sought in the context of the present invention.
• the process of the present invention makes it possible, unexpectedly, to produce covering films of adjustable thickness, greater than the molecular monolayer, that is to say films whose thickness is greater or much greater than the greatest dimension of the diazonium salt molecule used as a precursor to obtain the film.
• the working electrode that is to say the surface on which the film is grafted
• the counter electrode can be in contact with the same solution or else with different solutions during the 'electrografting.
• the present invention supplied therefore also a process for grafting and growing a conductive organic film on a conductive surface or semiconductive electricity by electroreduction of a diazonium salt precursor of said organic film, comprising a first step of grafting and growth of the film by application of at least one protocol consisting in the electroreduction of a first diazonium salt on said electrically polarized surface with at least one more cathodic working potential than the electroreduction potential of the first diazonium salt diazonium, said potentials being measured with respect to the same reference electrode; and a second step of grafting and growing the film by electroreduction of a second diazonium salt different from said first diazonium salt.
• the films obtained according to the method of the present invention are electrically conductive, and are formed by growth on themselves as the application of the successive protocols.
• the films obtained according to the invention also have the advantage of being conductive both in solution and dry, even after successive rinses. These films are therefore capable of dual electrical conduction, that is to say that they are intrinsic conductors, due to their polyaromatic type structure, and can be doped by the electrolytic substances present in their synthesis solution or inserted subsequently. . According to the invention, it is therefore possible to add doping agents to the film synthesis medium.
• doping agents can be those conventionally 'used by those skilled in the art to dope organic polymers.
• the process of the present invention makes it possible to manufacture organic films which can, simultaneously, provide protection against the external environment, for example against corrosion, and / or offer a grafted coating having functional groups. organic materials such as those mentioned above and / or promote or maintain electrical conductivity on the surface of the treated objects.
• the films of the present invention have the advantage that it is possible to grow thereon films of electro-initiated polymers, in the same way as is done on metal surfaces.
• MMA ethyl methacrylate
• a coating such as a coating of metal, traditional conductive polymers, charged polymers, etc. can therefore be electrodeposited on the film of the present invention by any technique known to those skilled in the art.
• all types of compounds such as conductive films based on aryl diazonium, vinyl monomers, molecules with tight cycles, etc. can be electrografted onto the film of the present invention also by any technique known to those skilled in the art. job .
• the process of the present invention can be repeated on the aforementioned new layer.
• a layer of an insulating polymer can also be deposited on the conductive film.
• the method of the present invention can further comprise a step of depositing an insulating film on said organic conductive film.
• insulating polymers are cited in the examples below. Other polymers such as these could of course be used in the context of the present invention.
• the organic films obtained according to the present invention constitute a grafted protective coating, which resists anode potentials beyond the corrosion potential of the conductive surface on which they have been electro-grafted.
• the process of the present invention can therefore also comprise, for example, a step of depositing a film of a vinyl polymer by electropolymerization of the corresponding vinyl monomer on the conductive polymer film.
• the process of the present invention can also be used to produce organic / conductive interfaces of great solidity.
• the organic films of the present invention are conductive at any thickness. When they are sparingly crosslinked, they can constitute "conductive sponges", with a conductive surface with an apparent area much greater than the original surface on which they are grafted. This allows a much denser functionalization than on the starting surface on which they are grafted.
• the method of the present invention also makes it possible to improve the solidity of interface between this polymer and metal via interpenetrating networks. Indeed, according to the invention, it is for example possible to electropolymerize monomers, such as vinyl monomers, tight cycle molecules, precursors of other conductive polymers etc., on the films of the present invention.
• monomers such as vinyl monomers, tight cycle molecules, precursors of other conductive polymers etc.
• the present invention makes it possible to establish two very solid interfaces metal / electro-grafted diazonium layer and layer of electro-grafted diazonium / polymer, where a direct polymer / metal interface would have been less solid by the methods of 1 prior art.
• the present invention consequently makes it possible to produce grafted and conductive organic coatings, of adjustable thickness, on conductive or semi-conductive surfaces.
• the process of the present invention can for example be used to protect non-noble metals against external aggressions, such as those produced by chemical agents, such as corrosion etc.
• This original protection conferred by the process of the invention can, for example, prove to be particularly advantageous in connection technology or contact technology, where the electrical conduction properties are improved and / or preserved.
• the method of the present invention can for example be used for the manufacture of localized conductive coatings, for example for microelectronics, its techniques and its applications such as new generations of inkjet printer heads, electronic sensors usable in vivo, interventional or implantable, biochips, microfluidics, lab-on-chips, etc.
• the process of the present invention can, for example, be used for the manufacture of conductive organic layers, the electrical potential of which can be controlled a posteriori, to serve for piloting, on a molecular scale, various physicochemical properties. of these films.
• This setting of the conductive film can for example be used to trigger any electrochemical reaction known to those skilled in the art, such as, for example, the electrodeposition of metals, polymers, charged or not, or redox of any redox couple having a standard potential compatible with the stability of the film, or alternatively, the electro-expulsion, by electrostatic repulsion, of charged species such as polymers, molecules, atomic ions, etc. , deposited on the surface of the conductive film, for example by non-specific adsorption.
• the method of the present invention may for example be used to manufacture underlayers grafted opaque, on all types of surfaces' conductive or semiconductive on which can perform all types of functionalization, and in particular those using electrochemistry, such as, for example, 1 electro-deposition, 1 electro-grafting of vinyl monomers, of tight cycles, of diazonium salts, of salts of carboxylic acids, of alkyries, of Grignard derivatives etc.
• This undercoat can thus constitute a quality primer for the re-metallization of objects, or for electro-grafting of functional groups, for example in the field of biomedical, biotechnologies, chemical sensors, instrumentation etc.
• the organic films based on diazonium salts of the present invention are conductive at any thickness.
• the present invention can therefore be used for example in the manufacture of an encapsulating coating for electronic components, in the manufacture of a hydrophilic coating, in the manufacture of a biocompatible coating, for the manufacture of a film usable as as an adhesion primer, as an organic post-functionalization support, as a coating with optical absorption properties or as a coating with stealth properties.
• FIGURES - Figure 1 Graphical representation of the voltammetric responses of a 10 "4 mol / 1 solution of 4-nitrophenyl diazonium tetrafluoroborate in acetonitrile, in the presence of 5 ⁇ 10 2" mol / 1 of TEAP, on a platinum electrode.
• the counter electrode is also a platinum electrode, and the reference electrode an Ag / Ag + electrode.
• Figure 9 Voltammograms of potential scans in a solution of 4-bromobenzyl diazonium tetrafluoroborate in acetonitrile, obtained by polarization of a platinum electrode.
• Tr (%) indicates the transmittance in percentage
• S has the aromatic substitutions (fig.2)
• N 0 the wave number in cm "1
• CPS indicates the number of strokes per second (number of electrons of an energy given when recording the XPS spectrum)
• ⁇ i indicates the binding energy in eV
• U V / Ag + / Ag
• I the intensity in mA.
• a platinum electrode is polarized, in voltammetric conditions, in a solution containing 10 "3 mol / l of 4-nitrophenyl diazonium tetrafluoroborate and 5 ⁇ 10 -2 mol / 1 of tetraethyl ammonium perchlorate (TEAP) acetonitrile.
• TEAP tetraethyl ammonium perchlorate
• IR and XPS infrared and XPS (Nls region) spectra of the 30 nm sample are shown in Figures 2 and 3 appended, respectively. They show the presence of an organic film still comprising nitro groups (IR), at least part of which has been modified, since two types of nitrogen are identified (XPS). In addition to the nitrogen measured at 406.3 eV which correspond to the nitro groups, there is a very intense component around 400 eV, which can correspond to nitrogen groups, probably reduced (NH 2 or N ⁇ N) and involved in the links between aromatic cycles of successive layers.
• Such structures would be compatible with the formation of a thick film, and the thickness of which increases with the number of voltametric scans, that is to say with the charge having passed through the circuit.
• a platinum electrode is polarized, under voltammetric conditions, in a solution containing 10 "3 mol / l of 4-bromobenzyl diazonium tetrafluoroborate and 5 ⁇ 10 " 2 mol / 1 of tetraethyl ammonium perchlorate (TEAP) in acetonitrile.
• TEAP tetraethyl ammonium perchlorate
• the potential sweeps are applied from + 0.5 V / (Ag + / Ag) to - 2.5 V / (Ag + / Ag), at - 20 mV / s, as shown in Figure 9.
• FIG. 9 represents voltammograms obtained for the first 4 potential scans, referenced 1, 2, 3 and 4 respectively, of the solution of 4-bromobenzyl diazonium tetrafluoroborate in acetonitrile.
• the reference 0 indicates the result obtained with the solution containing only the support electrolyte.
• the peak towards - 0.25 V / (Ag + / Ag) is that of the reduction of the diazonium salt, that towards - 2.25 V / (Ag + / Ag) is due to the reduction of the benzyl groups grafted on the area. It is observed that the intensity of this last peak increases as a function of the number of scans, which indicates the thickening of the film.
• a thickness of 5 nm is measured after 1 scan, 50 nm after 10 scans and 150 nm after 20 scans.
• a platinum electrode is polarized, under intentiostatic conditions, in a solution containing
• EXAMPLE 4 ELECTRIC CONDUCTION OF THE FILMS
• the slides covered with an electro-grafted film of Example 1 are immersed in a solution of acetonitrile alone, containing 5.10 "2 mol / 1 of tetraethyl ammonium perchlorate (TEAP). are again used as cathodes, and they are subjected to a series of scans between - 0.1 V / (Ag + / Ag) and - 2.0 V / (Ag + / Ag), at speeds between —50 and -500 mV / s.
• TEAP tetraethyl ammonium perchlorate
• the intensities of the voltammetric waves vary linearly with the scanning speed: this shows that these nitro groups are not subjected to diffusion, but behave as if they were adsorbed on the surface of the electrode.
• FIG. 6 the global spectra (graphs on the left) (all heart levels) and the heart level spectra of nitrogen (graphs on the right) are shown (nitro at 406 eV, polymer at 400eV) relating to the elimination of the NO 2 groups from the organic film obtained by electrografting nitrophenyldiazonium tetrafluoroborate, by subsequent electrochemical reduction.
• nitro at 406 eV polymer at 400eV
• FIG. 7a) represents an initial spectrum of an organic film obtained by electrografting of 30nm paranitrophenyl diazonium tetrafluoroborate
• FIG. 7b) represents a spectrum of the film of FIG. 7a) after electrochemical elimination of the nitro groups.
• the film has retained its initial thickness as evidenced by the bands relating to the polymer skeleton and the visual examination. These results were obtained from 30 nm films electrografted by voltametry.
• a platinum electrode is polarized under voltammetric conditions in a solution containing
• a rapid gain in thickness is observed as a function of the number of potential scans, as indicated in example 2, while the surface is clearly not passivated: the peak located towards - 0.25 V / (Ag + / Ag ) corresponding to the electro-reduction and grafting of the diazonium salts is always present, while a covering film is observed on the slide.
• MMA at 2 mol / 1 in acetonitrile containing 5.10 "2 mol / 1 of tetraethyl ammonium perchlorate (TEAP). It is again used as cathode, and it is subjected to a series of 10 scans between +0.3 V (Ag + / Ag) and -2.7 V (Ag + / Ag), at a scanning speed of -100 mV / s.
• TEAP tetraethyl ammonium perchlorate
• PMMA polymethylmethacrylate
• Figure 8 attached shows the infrared spectrum to identify the structure of the polymer formed, and observe the disappearance of nitro groups.
• Figure 10 is an infrared spectrum (Tr (%)) as a function of frequency (F) (cm "1 ).
• the top spectrum (BB) is that of a grafted bromo benzyl film on a gold surface according to the process of the present invention from 4-bromobenzyl diazonium tetrafluoroborate
• the bottom spectrum (PMMA) corresponds to the previous sample on which a PMMA film is grafted.
• EXAMPLE 7 INTERPENETRATION BETWEEN AN ELECTRO-GRAFTED CONDUCTIVE ORGANIC FILM AND AN ELECTRO-GRAFTED VINYL POLYMER FILM.
• Example 5 On the same bare platinum surface as that which was used in Example 5, that is to say on a platinum surface not previously covered with an organic conductive film, a protocol identical to that of Example 5 the production of a PMMA film about 30 nm thick, that is to say much less than the 80 nm obtained on a platinum surface covered with a diazos film.
• This result reproducible, in particular on other surfaces, is probably due to the fact that: (i) the diazos film is at least swollen by the synthetic solvent in which the electro-initiation of the vinyl is carried out; (ii) the film is conductive throughout its thickness, as shown in Example 6 above.
• This example illustrates the dry electrical conductivity of organic diazonium films.
• the films being thin, the measurements were carried out by optical methods rather than by directly dielectric methods. Indeed, the dielectric measurements are carried out with mechanical contact between the film and a metal surface serving as a probe.
• the film can be pierced at the time of contact between the probe and the sample, which has the effect of shorting the probe and the surface carrying the film. This accident, which is difficult to detect, has the consequence of finding any conductive coating. This type of measure is therefore not always convincing.
• the refractive index (n) and the extinction coefficient (k) of the films of the present invention are measured by ellipsometric electrochemical impedance spectroscopy.
• the same measurements are also carried out on films of vinyl polymers of similar thicknesses, which are known to be insulating. As the results show below, it appears: that the diazonium films give extinction coefficients k of the order of 0.4 to 0.5;
• coefficients k of this order are the same as those of the coatings obtained from conductive polymers such as polypyrrole (k ⁇ 0, 5) ... etc
• the extinction measurements are carried out by spectroscopic ellipsometry.
• the inventors proceeded by regression of the ellipsometric measurements using a complex smoothing software with a non-dispersive law, then with a model of Lorentz oscillators . The consistency of the results was checked with spectrophotometric measurements.
• optical extinction coefficients k were measured for two films obtained by electro-reduction of para-nitrophenyldiazonium tetrafluoroborate, which are compared with those of conductive coatings (gold, platinum, polypyrrole) as well as those of insulating coatings (PMAN, PMMA).
• the different thicknesses are obtained by varying the number of voltammetric scans; two films obtained by electro-reduction of a 10 " 3M solution of para-nitrophenyldiazonium tetrafluoroborate (PNPD) in anhydrous acetonitrile on platinum electrode, in the presence 5.10 "2 M TEAP (Tetra-Ethyl Ammonium Perchlorate) as support electrolyte. Potential scans are applied from + 0.3 V / (Ag + / Ag) to - 2.9 V / (Ag + / Ag) , at - 200 mV / s. Two films, of respective thicknesses 3 (OlOlPt ⁇ ) and 30 nm (0101Ptl4) so nt obtained by this protocol.
• PNPD para-nitrophenyldiazonium tetrafluoroborate
• Potential scans are applied from + 0.3 V / (Ag + / Ag) to - 2.9 V / (Ag
• the films obtained by electro-reduction of aryl diazonium salts therefore have good optical characteristics of conductors, and absorb significantly.
• EXAMPLE 9 DUAL LAYER OF ORGANIC CONDUCTIVE FILMS
• DUAL LAYER OF ORGANIC CONDUCTIVE FILMS it is illustrated that it is possible to produce organic multilayers from diazonium salts of different natures using the process of the present invention.
• TEAP tetraethyl ammonium perchlorate

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